Theta temperature Cellulose

Fig. 5.9. Comparison of extinction angle curves of high molecular weight fractions of polystyrene and cellulose tricarbanilate, using linear scales and reduced shear rate For data on polystyrene Taps. No. 5 and solvents see Table 3.2. (n) Taps. No. 5 in methyl (4-bromo-phenyl carbinol) at 18° C (theta-temperature), (V) the same at 50° C, (o) Taps. No. 5 in monobromo benzene at 25° C, ( ) cellulose tricarbanilate M = 720,000 in benzophenone at 55° C (jy = 4.70 cps) and (a) at...

Table 8. Concentration dependent parameters p, and p2 in the y parameter, Flory s theta temperature 9, and the entropy parameter J/ of cellulose diacetate, determined by different methods611... 

One of the main features of nonionic water-soluble cellulose derivatives is that they exhibit, like some other polyethers, an inverse solubility-temperature behavior, i.e. there is phase separation on heating above the so-called lower critical solution temperature (LCST). The temperature at which a polymer-rich phase separates is normally referred to as the cloud point (CP). For ideal solutions, this temperature corresponds to the theta-temperature. Actually, for some derivatives, the cloud point may be preceded, if the concentration is not too low, by a sol-gel transformation with an increase in viscosity and possibly formation of liquid crystals (see Sect. 3.5). As it will be seen later, this reversible thermotropic behavior may be detrimental to the performance of the derivatives or can be advantageneously utilized to develop applications. 

PAN Panina, N.I., Lozgacheva, V.P., and Averianova, V.M., Mactomolecular parameters of cellulose acetates near theta-temperature (Russ.), Vysokomol. Soedin., Ser. B, 19, 786, 1977. 

The Mandelkern-Flory viscosity data for cellulose tributyrate are plotted according to Eq. (58) in Fig. 18. It is seen that the line for the viscosities in the good solvent methyl ethyl ketone at 30° C passes without strain to the same intercept as the lines for the two high-temperature theta solvents. The intercept gives K = (9.7 1.5) 10-4 and a = 1.79 0.10, as listed in Table 9. Although, as discussed in the... 

It is well known that [r ] of most CD solutions decreases significantly with increasing temperature 80,82,83,86 90 103 109). Even in theta solvents, this effect has been observed for cellulose tricaprylate 104> and CTCp 86). This finding is in sharp contrast with what is known for vinyl polymers. 

Figure 3.5 illustrates the determination of the Flory 0-temperature for cellulose tricaproate dissolved in dimethylformamide (25). Table 3.6 presents a selected list of polymers and their theta solvents (26). 

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